Particles based electrodes and methods of making same

ABSTRACT

A coated electrode is provided for use in energy storage devices. The coated electrode comprises a dry particles that are fibrillized.

RELATED APPLICATIONS

The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 10/817,589, filed Apr. 2, 2004.

FIELD OF THE INVENTION

The present invention relates generally to the field of coating ofstructures for use in energy storage devices. More particularly, thepresent invention relates to capacitor structures and methods that usedry fibrillized fluoropolymers.

BACKGROUND INFORMATION

Double-layer capacitors, also referred to as ultracapacitors andsuper-capacitors, are energy storage devices that are able to store moreenergy per unit weight and unit volume than capacitors made withtraditional technology.

Double-layer capacitors store electrostatic energy in a polarizedelectrode/electrolyte interface layer. Double-layer capacitors includetwo electrodes, which are separated from contact by a porous separator.The separator prevents an electronic (as opposed to an ionic) currentfrom shorting the two electrodes. Both the electrodes and the porousseparator are immersed in an electrolyte, which allows flow of the ioniccurrent between the electrodes and through the separator. At theelectrode/electrolyte interface, a first layer of solvent dipole and asecond layer of charged species is formed (hence, the name“double-layer” capacitor).

Although, double-layer capacitors can theoretically be operated atvoltages as high as 4.0 volts and possibly higher, current double-layercapacitor manufacturing technologies limit nominal operating voltages ofdouble-layer capacitors to about 2.5 to 2.7 volts. Higher operatingvoltages are possible, but at such voltages undesirable destructivebreakdown begins to occur, which in part may be due to interactions withimpurities and residues that can be introduced during manufacture. Forexample, undesirable destructive breakdown of double-layer capacitors isseen to appear at voltages between about 2.7 to 3.0 volts. Double-layercapacitor can also provide high capacitance on the order of 0.1 to 5000Farads in relatively small form factor housings.

Known capacitor electrode fabrication techniques utilize coating andextrusion processes. Both processes utilize binders such as polymers orresins to provide cohesion between the surface areas of the particlesused.

In the coating process, the binder is dissolved in an appropriatesolvent, typically organic, aqueous or blends of aqueous and organics,and mixed with the conductive material, such as carbon, to form aslurry. The slurry is then coated through a doctor blade or a slot dieonto the current collector, and the resulting electrode is dried toremove the solvent. Among the numerous polymers and copolymers that canbe used as a binder in the coating process, most of them suffer from alack of stability when a subsequent electrolyte solvent is used toimpregnate a final capacitor product. This is especially true when thesolvent is an organic one and the working or storage temperature ishigher than 65° C. Instability of the binder can lead to a prematurefailure of an electrode and, thus a capacitor.

Typical extrusion processes use the fibrillation properties of certainpolymers to provide a matrix for embedded conductive material. Some ofthe polymers in the family of fluoropolymers, such aspolytetrafluoroethylene (PTFE), are particularly inert and stable in thecommon electrolyte solvents used in double-layer capacitors, even thoseusing organic solvent at high working or storage temperatures. Thus, thestability of an electrode made using PTFE can be higher than those madewith other binders. Polymers and similar ultra-high molecular weightsubstances capable of fibrillization are also commonly referred to as“fibrillizable binders” or “fibril-forming binders.” Fibril-formingbinders find use with powder like materials. In one prior art process,fibrillizable binder and powder materials are mixed with solvent,lubricant, or the like, and the resulting wet mixture is subjected tohigh-shear forces to sufficiently fibrillize the binder particles. Inthe prior art, fibrillization of the binder particles produces fibrilsthat eventually allow formation of a matrix or lattice for supporting aresulting composition of matter. In the prior art, solvents, liquids,and processing aides are added so that subsequent shear forces appliedto a resulting mixture are sufficient to fibrillize the particles.During prior art extrusion and/or coating and/or subsequent calenderingstages, although fibrillization is known to occur, such processes alsocause a large number of the fibrillized binder particles to re/coalesceand be formed into agglomerates. As seen in FIG. 5, such agglomerationis seen and evidenced by the large smeared and individual globularstructures present in a final film product. The large number of suchre/coalesced binder particles results in a reduced final film integrityand performance.

In the prior art, the resulting additive based extruded product issubsequently processed in a high-pressure compactor, dried to remove theadditive, shaped into a needed form, and otherwise processed to obtainan end-product for the needed application. For purposes of handling,processing, and durability, desirable properties of the end producttypically depend on the consistency and homogeneity of the compositionof matter from which the product is made, with good consistency andhomogeneity being important requirements. Such desirable propertiesdepend on the degree of fibrillization of the polymer. Tensile strengthcommonly depends on both the degree of fibrillization of thefibrillizable binder, and the consistency of the fibril lattice formedby the binder within the material. When used as an electrode, internalresistance of an electrode film is also important.

Internal resistance may depend on bulk resistivity—volume resistivity onlarge scale—of the material from which an electrode film is fabricated.Bulk resistivity of the material is a function of the material'shomogeneity; the better the dispersal of the conductive carbon particlesor other conductive filler within the material, the lower theresistivity of the material. When electrode films are used incapacitors, such as double-layer capacitors, capacitance per unit volumeis yet another important characteristic. In double layer capacitors,capacitance increases with the specific surface area of the electrodefilm used to make a capacitor electrode. Specific surface area isdefined as the ratio of (1) the surface area of electrode film exposedto an electrolytic solution when the electrode material is immersed inthe solution, and (2) the volume of the electrode film. An electrodefilm's specific surface area and capacitance per unit volume arebelieved to improve with improvement in consistency and homogeneity.

Because fluoropolymers do not dissolve in most solvents, they are notsuited for use as a binder in conventional solvent based coatingprocesses. Because extrusion processes require large manufacturingequipment investments, it is often financially prohibitive for electrodemanufacturers to adopt manufacturing processes that take advantage ofthe benefits of using fluoropolymers as a binder. As such, it would bedesirable to use fluoropolymers in the manufacture of coated electrodes.

SUMMARY

In accordance with embodiments of the present invention, fibrillizablepolymers and methods of using in manufacture of energy storage devicesare described. The present invention provides methods for making longlasting, durable, and inexpensive energy storage devices, for example,capacitors. Fibrillization of the polymers may provided without the useof any processing additives. Further fibrillization may be provided toin other later steps. The present invention provides distinct advantageswhen compared to that of the coating based methods of the prior art. Ahigh throughput method for making more durable and more reliable coatingbased energy storage devices is provided.

In one embodiment, a method of making a slurry coated electrodecomprises dry blending dry carbon particles and dry binder to form a drymixture comprised of the dry carbon particles and the dry binder;liquefying the dry mixture with a solution to form a slurry; applyingthe slurry to a current collector; drying the slurry; and compacting thecurrent collector and slurry. The method may further comprise a step offibrillizing the mixture. The fibrillizing step may comprise dryfibrillizing the mixture. The fibrillizing step may comprise subjectingthe mixture to high shear forces. The fibrillizing step may utilize apressure. The pressure may comprise a pressure of more than 10 PSI. Thepressure may be applied during the step of compacting. The method mayfurther comprise the step of treating the current collector prior toapplying the slurry to improve adhesion between the current collectorand slurry. The step of treating the current collector may furthercomprise coating the current collector with a bonding agent prior toapplying the slurry. The step of treating the current collector mayfurther comprise roughening a surface of the current collector prior toapplying the slurry. The dry binder may comprise a fluoropolymer. Thefluoropolymer particles may comprise PTFE. The mixture may compriseconductive particles. The mixture may comprise activated carbonparticles. The mixture may comprise approximately 50% to 99% activatedcarbon. The mixture may comprise approximately 0% to 30% conductivecarbon. The mixture may comprise approximately 1% to 50% fluoropolymerparticles. The mixture may comprise approximately 80% to 95% activatedcarbon, approximately 0% to 15% conductive carbon, and approximately 3%to 15% fluoropolymer. The solution may comprise deionized water. Thecurrent collector may comprise aluminum. The step of applying thesuspension may comprise coating the current collector with the slurryusing a doctor blade, a slot die, or a direct or reverse gravureprocess.

In one embodiment, a blend of dry particles fibrillized for use in themanufacture of a coated electrode, comprising: a mixture of dryfibrillized dry carbon and dry binder particles. The dry binderparticles may comprise a polymer, wherein the dry carbon particlescomprise activated and conductive carbon. The binder may comprisefluoropolymer particles. The binder may comprise PTFE. The binder maycomprise particles subjected to pressure. The high pressure may be morethan about 10 PSI. The pressure may be applied by a jet mill. Thepressure may be applied by a roll-mill. The pressure may be applied by ahammer mill. The electrode may be an energy storage device electrode.The energy storage device may be a capacitor.

In one embodiment, an electrode comprises a dry blend of dry carbonparticles and dry binder particles subjected to high shear forces. Theblend may comprise approximately 50% to 99% activated carbon. The blendmay comprise approximately 0% to 30% conductive carbon. The blend maycomprise approximately 1% to 50% fluoropolymer. The blend may compriseapproximately 80% to 95% activated carbon, approximately 0% to 15%conductive carbon, and approximately 3% to 15% fluoropolymer. Theelectrode may comprise a capacitor electrode. The electrode may be adouble-layer capacitor electrode. The electrode may be a batteryelectrode. The electrode may be a fuel-cell electrode.

The electrode may further comprise a current collector, wherein thebinder and carbon particles are in the form of a coated dried slurry,wherein the slurry is coupled to the current collector.

In one embodiment, a capacitor product comprises a dry fibrillized blendof dry particles subjected to high shear forces, the particles includingbinder and carbon particles; and one or more current collector, whereinthe blend of dry particles are disposed onto the one or more currentcollector as a coating. Between the one or more current collector andthe dry particles may be disposed a bonding layer. The one or morecurrent collector may comprise aluminum. The one or more currentcollector may be shaped as a roll, wherein the roll is disposed withinthe housing. Within the housing may be disposed an electrolyte. Theelectrolyte may comprise acetonitrile.

In one embodiment, an energy storage device comprises fibrillizedelectrode means for providing coated electrode functionality in anenergy storage device.

In one embodiment, a capacitor, the capacitor comprises a housing; acover; a collector, the collector disposed in the housing, the collectorcomprising two ends, a first end coupled to the housing, a second endcoupled to the cover; a dried electrode slurry, the dried electrodeslurry disposed as a coating onto the collector, the dried electrodeslurry comprising a dry fibrillized blend of dry carbon and dry polymer,the dry fibrillized blend comprising of essentially no processingadditive; and an electrolyte, the electrolyte disposed in the housing.The capacitor may comprise a capacitance of greater than or equal to 0.1Farad.

Other embodiments, benefits, and advantages will become apparent upon afurther reading of the following Figures, Description, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a block diagram illustrating a method for making an energystorage device electrode.

FIG. 1 b is a high-level front view of a jet mill assembly used tofibrillize binder within a dry carbon particle mixture.

FIG. 1 c is a high-level side view of a jet mill assembly shown in FIG.1 b;

FIG. 1 d is a top view of the jet mill assembly shown in FIGS. 1 b and 1c.

FIG. 1 e is a high-level front view of a compressor and a compressed airstorage tank used to supply compressed air to a jet mill assembly.

FIG. 1 f is a high-level top view of the compressor and the compressedair storage tank shown in FIG. 1 e, in accordance with the presentinvention.

FIG. 1 g is a high-level front view of the jet mill assembly of FIGS. 1b-d in combination with a dust collector and a collection container.

FIG. 1 h is a high-level top view of the combination of FIGS. 1 f and 1g.

FIGS. 1 i, 1 j, and 1 k illustrate effects of variations in feed rate,grind pressure, and feed pressure on tensile strength in length, tensilestrength in width, and dry resistivity of electrode materials.

FIG. 1 m illustrates effects of variations in feed rate, grind pressure,and feed pressure.

FIG. 1 n illustrates effects of variations in feed rate, grind pressure,and feed pressure on capacitance.

FIG. 1 p illustrates effect of variation in feed pressure on internalresistance of electrodes, and on the capacitance of double layercapacitors using such electrodes.

FIG. 2 shows an apparatus for forming a coated electrode.

FIG. 3 is a representation of a rolled electrode coupled internally to ahousing.

FIG. 4 shows a SEM taken of dry particles that are formed by dryfibrillization step 20.

FIG. 5 illustrates a prior art additive based film that comprisessubstantial amounts of agglomerates of coalesced particles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to several embodiments of theinvention that are illustrated in the accompanying drawings. Inaccordance with embodiments of the present invention, fibrillizablepolymers and methods of using in manufacture of energy storage devicesare described. The present invention provides methods for making longlasting, durable, and inexpensive energy storage devices, for example,capacitors. Fibrillization of the polymers may effectuated without theuse of any processing additives. The present invention provides distinctadvantages when compared to that of the coating based methods of theprior art. A high throughput method for making more durable and morereliable coating based energy storage devices is provided.

In the embodiments that follow, it will be understood that reference tono-use and non-use of additive(s) in the manufacture of an energystorage device according to the present invention takes into accountthat electrolyte may be used during a final electrode electrolyteimmersion/impregnation step. An electrode electrolyteimmersion/impregnation step is typically utilized prior to providing afinal finished capacitor electrode in a sealed housing. Furthermore,even though additives, such as solvents, liquids, and the like, are notused in the dry fibrillization of polymers and dry particles inembodiments disclosed herein, during fibrillization, a certain amount ofimpurity, for example, moisture, may be absorbed or attach itself from asurrounding environment. Those skilled in the art will understand thatthe dry particles used with embodiments and processes disclosed hereinmay also, prior to their being provided by particle manufacturers as dryparticles, have themselves been pre-processed with additives, liquids,solvents, etc., and, thus, comprise one or more pre-process residuethereof. It is identified that even after one or more drying step, traceamounts of the aforementioned pre-process residues and impurities may bepresent in the dry fibrillization process steps described herein.

Referring now to FIG. 1 a, a block diagram illustrating a process formaking an energy device using dry fibrillized binder is shown. Theprocess shown in FIG. 1 a begins by dry blending dry carbon particlesand dry binder particles together. Those skilled in the art willunderstand that depending on particle size, particles can be describedas powders and the like, and that reference to particles is not meant tobe limiting to the embodiments described herein, which should be limitedonly by the appended claims and their equivalents. For example, withinthe scope of the term “particles,” the present invention contemplatespowders, spheres, platelets, flakes, fibers, nano-tubes, and otherparticles with other dimensions and other aspect ratios. In oneembodiment, dry carbon particles as referenced herein refers toactivated carbon particles 12 and/or conductive particles 14, and binderparticles 16 as referenced herein refers to an inert dry binder. In oneembodiment, conductive particles 14 comprise conductive carbonparticles. In one embodiment, conductive particles 14, may comprisegraphite. In one embodiment, it is envisioned that conductive particles14 may comprise a metal and/or other non-carbon material. In oneembodiment, dry binder 16 comprises a fibrillizable polymer, forexample, polytetrafluoroethylene (PTFE) particles. Other fibrillizablebinders envisioned for use herein include ultra-high molecular weightpolypropylene, polyethylene, co-polymers, polymer blends and the like.It is understood that the present invention should not be limited by thedisclosed or suggested binder, but rather, by the claims that follow. Inone embodiment, particular mixtures of particles 12, 14, and binder 16comprise about 50% to 99% activated carbon, about 0% to 30% conductivecarbon, and/or about 1% to 50% binder by weight. In a more particularembodiment, particle mixtures include about 80% to 90% activated carbon,about 0% to 15% conductive carbon, and about 3% to 15% binder by weight.In one embodiment, the activated carbon particles 12 comprise a meandiameter of about 10 microns. In one embodiment, the conductive carbonparticles 14 comprise a range of diameters of less than 20 microns. Inone embodiment, the binder particles 16 comprise a mean diameter ofabout 450 microns. Suitable carbon powders are available from a varietyof sources, including YP-17 activated carbon particles sold by KurarayChemical Co., LTD, Shin-hankyu Bldg. 9F Blvd. C-237, 1-12-39 Umeda,Kiata-ku, Osaka 530-8611, Japan; and BP 2000 conductive particles soldby Cabot Corp. 157 Concord Road, P.O. Box 7001, Billerica, Mass.01821-7001, Phone: 978 663-3455.

In step 18, particles of activated carbon, conductive carbon, and binderprovided during respective steps 12, 14, and 16 are dry blended togetherto form a dry mixture. In one embodiment, dry particles 12, 14, and 16are blended for 1 to 10 minutes in a V-blender equipped with a highintensity mixing bar until a uniform dry mixture is formed. Thoseskilled in the art will identify that blending time can vary based onbatch size, materials, particle size, densities, as well as otherproperties, and yet remain within the scope of the present invention.With reference to blending step 18, in one embodiment, particle sizereduction and classification can be carried out as part of the blendingstep 18, or prior to the blending step 18. Size reduction andclassification may improve consistency and repeatability of theresulting blended mixture and, consequently, of the quality of electrodefilms and electrodes fabricated therefrom.

Referring to FIG. 4, there is seen a SEM taken of dry particles that areformed by dry fibrillization step 20. After dry blending step 18, drybinder 16 within the dry particles is fibrillized in a dry fibrillizingstep 20. The dry fibrillizing step 20 is effectuated using a drysolventless and liquidless high shear technique. The high shear acts toenmesh, entrap, bind, and/or support the dry particles 12 and 14.However, as can be seen from FIG. 14, even at magnifications as high as100,000×, evidence of fibrillization in the form of fibrils isdifficult, if not impossible, to discern. Although fibrils seemingly arenot visible, it is conjectured that rather than the type of fibrilformation that occurs in coating and extrusion based processes, duringdry fibrillization step 20, dry binder in the form of macroscopicaggregates becomes pulverized by the energy imparted to the dryparticles to a size that fibrils are not visible. It is believed thatdry fibrillization causes a reduction of dry binder particles 20 totheir basic constituent size, which is known to those skilled in the artas a dispersion particle size. In one embodiment, such dispersion sizeis on the order of about 0.1 to 2 um. Pulverization of dry binder 16occurs when carbon or other dry non-binder material is added to the jetmill. The presence of particles other than binder acts as diluent thatdisperses the binder particles away from each other so that they cannotre/coalesce. At least in part, because dry binder particles aredispersed, they are unable to form agglomerates as occurs in the priorart.

As well, as seen in FIG. 4, at 100,000× magnification, at least somedispersion sized dry binder particles appear to have been deposited oradhered onto carbon particles. As defined herein a “weak” and/or notvisible form of fibrillization has occurred such that dry binder withinthe dry mixture has been pulverized and/or converted, at least in part,into dispersion sized particles that are of such short length and/orsmall size that they may act to provide the aforementioned enmeshing,entrapping, binding, and/or supporting functionality. Thus,fibrillization on the scale of one or more dispersion sized particle iscontemplated, wherein fibrillization may comprise a change in dimensionof such dispersion particle(s), which is within the scope of thedefinition of fibrillization as used by those skilled in the art whereinan elongation of binder particle or coalesced binder particles is knownto occur.

As further seen from FIG. 4, direct surface to surface contact existsbetween many of the dry carbon particles within the dry fibrillizedmixture of dry particles. It is believed that the weak fibrillizationdescribed above causes dry binder particles that have been reduced insize to be deposited onto and between the dry carbon particles and withsurface energies such that sufficient contact and adhesion between thecarbon articles can be maintained to provide enmeshment, entrapment,binding, and/or support to the mix of dry particles, and such that thedry particles can be later easily formed into a film as is describedfurther below. Such conclusions are supported by EDX sampling of the dryfibrillized powder during imaging of the dry fibrillized particles withan SEM. It has been identified by the present inventors from EDXanalysis that although dry binder 16 can be detected in the originalproportions that were present during step 18, the binder is in a fromthat is substantially changed from that originally introduced in step20. A typical SEM image taken of dry fibrillized carbon and binderparticles formed during step 20 shows only dry carbon particles.Although EDX shows that dry binder is present, it is in a form that doesnot appear to be imagable as fibril or in its originally introducedaggregate form, even using an SEM at 100000×. Nevertheless, the dryfibrillized mixture of dry particles at step 20 exhibits thecharacteristics of a homogeneous matrix that can be handled and formedinto a film as describe further below.

Referring to now to FIGS. 1 b, 1 c, and 1 d, there is seen,respectively, front, side, and top views of a jet mill assembly 100 usedto perform a dry fibrillization step 20. For convenience, the jet millassembly 100 is installed on a movable auxiliary equipment table 105,and includes indicators 110 for displaying various temperatures and gaspressures that arise during operation. A gas input connector 115receives compressed air from an external supply and routes thecompressed air through internal tubing (not shown) to a feed air hose120 and a grind air hose 125, which both lead and are connected to a jetmill 130. The jet mill 130 includes: (1) a funnel-like materialreceptacle device 135 that receives compressed feed air from the feedair hose 120, and the blended carbon-binder mixture of step 18 from afeeder 140; (2) an internal grinding chamber where the carbon-bindermixture material is processed; and (3) an output connection 145 forremoving the processed material. In the illustrated embodiment, the jetmill 130 is a 4-inch Micronizer® model available from Sturtevant, Inc.,348 Circuit Street, Hanover, Mass. 02339; telephone number (781)829-6501. The feeder 140 is an AccuRate® feeder with a digital dialindicator model 302M, available from Schenck AccuRate®, 746 E. MilwaukeeStreet, P.O. Box 208, Whitewater, Wis. 53190; telephone number (888)742-1249. The feeder includes the following components: a 0.33 cubic ft.internal hopper; an external paddle agitation flow aid; a 1.0-inch, fullpitch, open flight feed screw; a ⅛ hp, 90 VDC, 1,800 rpm, TENV electricmotor drive; an internal mount controller with a variable speed, 50:1turndown ratio; and a 110 Volt, single-phase, 60 Hz power supply with apower cord. The feeder 140 dispenses the carbon-binder mixture providedby step 18 at a preset rate. The rate is set using the digital dial,which is capable of settings between 0 and 999, linearly controlling thefeeder operation. The highest setting of the feeder dial corresponds toa jet mill output of about 12 kg per hour.

The feeder 140 appears in FIGS. 1 b and 1 d, but has been omitted fromFIG. 1 c, to prevent obstruction of view of other components of the jetmill 130. The compressed air used in the jet mill assembly 100 isprovided by a combination 200 of a compressor 205 and a compressed airstorage tank 210, illustrated in FIGS. 1 e and 1 f; FIG. 1 e is a frontview and FIG. 1 f is a top view of the combination 200. The compressor205 used in this embodiment is a GA 30-55C model available from AtlasCopco Compressors, Inc., 161 Lower Westfield Road, Holyoke, Mass. 01040;telephone number (413) 536-0600. The compressor 205 includes thefollowing features and components: air supply capacity of 180 standardcubic feet per minute (“SCFM”) at 125 PSIG; a 40-hp, 3-phase, 60 HZ, 460VAC premium efficiency motor; a WYE-delta reduced voltage starter;rubber isolation pads; a refrigerated air dryer; air filters and acondensate separator; an air cooler with an outlet 206; and an aircontrol and monitoring panel 207. The 180-SCFM capacity of thecompressor 205 is more than sufficient to supply the 4-inch Micronizer®jet mill 130, which is rated at 55 SCFM. The compressed air storage tank210 is a 400-gallon receiver tank with a safety valve, an automaticdrain valve, and a pressure gauge. The compressor 205 providescompressed air to the tank 205 through a compressed air outlet valve206, a hose 215, and a tank inlet valve 211.

In one embodiment, it is identified that the compressed air providedunder pressure by compressor 205 is preferably as dry as possible. Inone embodiment, a range of dew point for the air is about −20 to −40degrees F., and water content of less than about 20 ppm; other rangesare also within the scope of this invention. Although discussed as beingeffectuated by pressurized air, it is understood that other sufficientlydry gases are envisioned as being used to fibrillize binder particlesutilized in embodiments of the present invention, for example, oxygen,nitrogen, helium, and the like.

In the jet mill 130, the carbon-binder mixture is inspired by venturiand transferred by the compressed feed air into a grinding chamber,where the fibrillization of the mixture takes place. The grindingchamber, which has a generally cylindrical shape, includes one or morenozzles placed circumferentially. The nozzles discharge the compressedgrind air that is supplied by the grind air hose 125. The compressed airjets injected by the nozzles accelerate the carbon-binder particles andcause predominantly particle-to-particle collisions, although someparticle-wall collisions also take place. The collisions dissipate theenergy of the compressed air relatively quickly, fibrillizing the drybinder 16 within the mixture by causing size reduction of the aggregatesand agglomerates of originally introduced dry particles and so as toadhere and embed carbon particle 12 and 14 within a resulting lattice ofparticles formed by the fibrillized binder. The colliding particles 12,14, and 16 spiral towards the center of the grinding chamber and exitthe chamber through the output connection 145.

Referring now to FIGS. 1 g and 1 h, there are seen front and top views,respectively, of the jet mill assembly 100, a dust collector 160, and acollection container 170. In one embodiment, the fibrillizedcarbon-binder particles that exit through the output connection 145 areguided by a discharge hose 175 from the jet mill 130 into a dustcollector 160. In the illustrated embodiment, the dust collector 160 ismodel CL-7-36-11 available from Ultra Industries, Inc., 1908 DeKovenAvenue, Racine, Wis. 53403; telephone number (262) 633-5070. Within thedust collector 160 the output of the jet mill 130 is separated into (1)air and dust, and (2) a dry fibrillized carbon-binder particle mixture20. The carbon-binder mixture is collected in the container 170, whilethe air is filtered by one or more filters to remove the dust, and thendischarged. The filters, which may be internal or external to the dustcollector 160, are periodically cleaned, and the dust is discarded.Operation of the dust collector is directed from a control panel 180.

It has been identified that a dry compounded material, which is providedby dry fibrillization step 20, retains its homogeneous particle likeproperties for a limited period of time. In one embodiment, because offorces, for example, gravitational forces exerted on the dry particles12, 14, and 16, the compounded material begins to settle such thatspaces and voids that exist between the dry particles 12, 14, 16 afterstep 20 gradually become reduced in volume. In one embodiment, after arelatively short period of time, for example 10 minutes or so, the dryparticles 12, 14, 16 compact together and begin to form clumps or chunkssuch that the homogeneous properties of the compounded material may bediminished and/or such that downstream processes that require freeflowing compounded materials are made more difficult to achieve.

Accordingly, in one embodiment, it is identified that a dry compoundedmaterial as provided by step 20 should be utilized before itshomogeneous properties are no longer sufficiently present and/or thatsteps are taken to keep the compounded material sufficiently aerated toavoid clumping. It should be noted that the specific processingcomponents described so far may vary as long as the intent of theembodiments described herein is achieved. For example, techniques andmachinery that are envisioned for potential use to provide high shearand/or pressure forces to effectuate a dry fibrillization step 20include jet-milling, pin milling, impact pulverization, roll milling,and hammer milling, and other techniques and apparatus. Further inexample, a wide selection of dust collectors can be used in alternativeembodiments, ranging from simple free-hanging socks to complicatedhousing designs with cartridge filters or pulse-cleaned bags. Similarly,other feeders can be easily substituted in the assembly 100, includingconventional volumetric feeders, loss-weight volumetric feeders, andvibratory feeders. The size, make, and other parameters of the jet mill130 and the compressed air supply apparatus (the compressor 205 and thecompressed air storage tank 210) may also vary and yet be within thescope of the present invention.

The present inventors have performed a number of experiments toinvestigate the effects of three factors in the operation of jet millassembly 100 on qualities of the dry compounded material provided by dryfibrillization step 20, and on compacted electrode films fabricatedtherefrom. The three factors are these: (1) feed air pressure, (2) grindair pressure, and (3) feed rate. The observed qualities included tensilestrength in width (i.e., in the direction transverse to the direction ofmovement of a electrode film in a high-pressure calender during acompacting process); tensile strength in length (i.e., in the directionof the film movement); resistivity of the dry jet mill processed mixtureprovided by dry fibrillization step 20; internal resistance of compactedelectrode films; and specific capacitance achieved in a double layercapacitor application. Resistance and specific capacitance values wereobtained for both charge (up) and discharge (down) capacitor cycles.

The design of experiments (“DOE”) included a three-factorial, eightexperiment investigation performed with electrode films dried for 3hours under vacuum conditions at 160 degrees Celsius. Five or sixsamples were produced in each of the experiments, and values measured onthe samples of each experiment were averaged to obtain a more reliableresult. The three-factorial experiments were performed at a dew point ofabout −40 degrees F., water content 12 ppm and included the followingpoints for the three factors:

-   1. Feed rate was set to indications of 250 and 800 units on the    feeder dial used. Recall that the feeder rate has a linear    dependence on the dial settings, and that a full-scale setting of    999 corresponds to a rate of production of about 12 kg per hour (and    therefore a substantially similar material consumption rate). Thus,    settings of 250 units corresponded to a feed rate of about 3 kg per    hour, while settings of 800 units corresponded to a feed rate of    about 9.6 kg per hour. In accordance with the standard vernacular    used in the theory of design of experiments, in the accompanying    tables and graphs the former setting is designated as a “0” point,    and the latter setting is designated as a “1” point.-   2. The grind air pressure was set alternatively to 85 psi and 110    psi, corresponding, respectively, to “0” and “1” points in the    accompanying tables and graphs.-   3. The feed air pressure (also known as inject air pressure) was set    to 60 and 70 psi, corresponding, respectively, to “0” and “1”    points.

Turning first to tensile strength measurements, strips of standard widthwere prepared from each sample, and the tensile strength measurement ofeach sample was normalized to a one-mil thickness. The results fortensile strength measurements in length and in width appear in Tables 2and 3 below.

TABLE 2 Tensile Strength in Length NORMALIZED TENSILE TENSILE STRENGTHFACTORS SAMPLE STRENGTH IN Exp. Feed Rate, Grind DOE THICKNESS IN LENGTHLENGTH No. psi, Feed psi POINTS (mil) (grams) (g/mil) 1 250/85/60 0/0/06.1 123.00 20.164 2 250/85/70 0/0/1 5.5 146.00 26.545 3 250/110/60 0/1/06.2 166.00 26.774 4 250/110/70 0/1/1 6.1 108.00 17.705 5 800/85/60 1/0/06.0 132.00 22.000 6 800/85/70 1/0/1 5.8 145.00 25.000 7 800/110/60 1/1/06.0 135.00 22.500 8 800/110/70 1/1/1 6.2 141.00 22.742

TABLE 3 Tensile Strength in Width Normalized Factors Tensile Tensile(Feed Rate, Sample Strength Strength Exp. Grind psi, DOE Thickness inLength in Length No. Feed psi) Points (mil) (grams) (g/mil) 1 250/85/600/0/0 6.1 63.00 10.328 2 250/85/70 0/0/1 5.5 66.00 12.000 3 250/110/600/1/0 6.2 77.00 12.419 4 250/110/70 0/1/1 6.1 59.00 9.672 5 800/85/601/0/0 6.0 58.00 9.667 6 800/85/70 1/0/1 5.8 70.00 12.069 7 800/110/601/1/0 6.0 61.00 10.167 8 800/110/70 1/1/1 6.2 63.00 10.161

Table 4 below presents resistivity measurements of a jet milled dryblend of particles provided by dry fibrillization step 20. Note that theresistivity measurements were taken before the mixture was processedinto an electrode film.

TABLE 4 Dry Resistance Factors Exp. (Feed Rate, Grind psi, DOE DRYRESISTANCE No. Feed psi) Points (Ohms) 1 250/85/60 0/0/0 0.267 2250/85/70 0/0/1 0.229 3 250/110/60 0/1/0 0.221 4 250/110/70 0/1/1 0.2125 800/85/60 1/0/0 0.233 6 800/85/70 1/0/1 0.208 7 800/110/60 1/1/0 0.2418 800/110/70 1/1/1 0.256

Referring now to FIGS. 1 i, 1 j, and 1 k, there are illustrated theeffects of the three factors on the tensile strength in length, tensilestrength in width, and dry resistivity. Note that each end-point for aparticular factor line (i.e., the feed rate line, grind pressure line,or inject pressure line) on a graph corresponds to a measured value ofthe quality parameter (i.e., tensile strength or resistivity) averagedover all experiments with the particular key factor held at either “0”or “1” as the case may be. Thus, the “0” end-point of the feed rate line(the left most point) represents the tensile strength averaged overexperiments numbered 1-4, while the “1” end-point on the same linerepresents the tensile strength averaged over experiments numbered 4-8.As can be seen from FIGS. 1 i and 1 j, increasing the inject pressurehas a moderate to large positive effect on the tensile strength of anelectrode film. At the same time, increasing the inject pressure has thelargest effect on the dry resistance of the powder mixture, swamping theeffects of the feed rate and grind pressure. The dry resistancedecreases with increasing the inject pressure. Thus, all three qualitiesbenefit from increasing the inject pressure.

In Table 5 below we present data for final capacitances measured indouble-layer capacitors utilizing electrode films made from dryfibrillized particles as described herein by each of the 8 experiments,averaged over the sample size of each experiment. Note that C_(up)refers to the capacitances measured when charging double-layercapacitors, while C_(down) values were measured when discharging thecapacitors. As in the case of tensile strength data, the capacitanceswere normalized to the thickness of the electrode film. In this case,however, the thicknesses have changed, because the film has undergonecompression in a high-pressure nip during a process of bonding the filmto a current collector. It is noted in obtaining the particular resultsof Table 5, the electrode film was bonded to a current collector by anintermediate layer of coated adhesive. Normalization was carried out tothe standard thickness of 0.150 millimeters.

TABLE 5 C_(up) and C_(down) Factors (Feed Rate, Sample NORMALIZED Exp.Grind psi, DOE Thickness C_(up) Normalized C_(down) C_(down) No. Feedpsi) Points (mm) (Farads) C_(up) (Farads) (Farads) (Farads) 1 250/85/600/0/0 0.149 1.09 1.097 1.08 1.087 2 250/85/70 0/0/1 0.133 0.98 1.1050.97 1.094 3 250/110/60 0/1/0 0.153 1.12 1.098 1.11 1.088 4 250/110/700/1/1 0.147 1.08 1.102 1.07 1.092 5 800/85/60 1/0/0 0.148 1.07 1.0841.06 1.074 6 800/85/70 1/0/1 0.135 1.00 1.111 0.99 1.100 7 800/110/601/1/0 0.150 1.08 1.080 1.07 1.070 8 800/110/70 1/1/1 0.153 1.14 1.1181.14 1.118

In Table 6 we present data for resistances measured in each of the 8experiments, averaged over the sample size of each experiment. Similarlyto the previous table, R_(up) designates resistance values measured whencharging double-layer capacitors, while R_(down) refers to resistancevalues measured when discharging the capacitors.

TABLE 6 R_(up) and R_(down) Factors Sample (Feed Rate, Thick- ElectrodeElectrode Exp. Grind psi, DOE ness Resistance Resistance No. Feed psi)Points (mm) R_(up) (Ohms) R_(down) (Ohms) 1 250/85/60 0/0/0 0.149 1.731.16 2 250/85/70 0/0/1 0.133 1.67 1.04 3 250/110/60 0/1/0 0.153 1.631.07 4 250/110/70 0/1/1 0.147 1.64 1.07 5 800/85/60 1/0/0 0.148 1.681.11 6 800/85/70 1/0/1 0.135 1.60 1.03 7 800/110/60 1/1/0 0.150 1.801.25 8 800/110/70 1/1/1 0.153 1.54 1.05

To help visualize the above data and identify the data trends, wepresent FIGS. 1 m and 1 n, which graphically illustrate the relativeimportance of the three factors on the resulting R_(down) and normalizedC_(up). Note that in FIG. 1 m the Feed Rate and the Grind Pressure linesare substantially coincident. Once again, increasing the inject pressurebenefits both electrode resistance R_(down) (lowering it), and thenormalized capacitance C_(up) (increasing it). Moreover, the effect ofthe inject pressure is greater than the effects of the other twofactors. In fact, the effect of the inject pressure on the normalizedcapacitance overwhelms the effects of the feed rate and the grindpressure factors, at least for the factor ranges investigated.

Additional data has been obtained relating C_(up) and R_(down) tofurther increases in the inject pressure. Here, the feed rate and thegrind pressure were kept constant at 250 units and 110 psi,respectively, while the inject pressure during production was set to 70psi, 85 psi, and 100 psi. Bar graphs in FIG. 1 p illustrate these data.As can be seen from these graphs, the normalized capacitance C_(up) waslittle changed with increasing inject pressure beyond a certain point,while electrode resistance displayed a drop of several percentage pointswhen the inject pressure was increased from 85 psi to 100 psi. Theinventors herein believe that increasing the inject pressure beyond 100psi would further improve electrode performance, particularly bydecreasing internal electrode resistance. In other embodiments, withother types of particles and particle composition it has been identifiedthat 10 psi may be used during a dry fibrillization step.

Although dry blending 18 and dry fibrillization step 20 have beendiscussed herein with reference to specific apparatus, it is envisionedthat steps 18 and 20 could be conducted in one step wherein an apparatusreceives dry particles 12, 14, and/or 16 as separate streams to mix theparticles and thereafter fibrillize the particles. Accordingly, it isunderstood that the embodiments herein should not be limited by steps 18and 20, but by the claims that follow. Furthermore, the precedingparagraphs describe in considerable detail inventive methods for dryfibrillizing dry carbon and dry binder mixtures, however, neither thespecific embodiments of the invention as a whole, nor those of itsindividual features should limit the general principles describedherein, which should be limited only by the claims that follow.

It is identified that to achieve a sufficient level of fibrillization,sufficiently high forces may be applied to a dry particle mixture. Asdescribed above, such or similar forces may be applied during a dryfibrillization step 20, however, as described below, they can also beapplied during one or more other electrode formation step.

Numerous benefits may derive from non-use of prior art additivesincluding: reduction of process steps and processing apparatus, increasein throughput, the elimination or substantial reduction of residue andimpurities that can derive from the use of additives and additive-basedprocess steps, a substantial reduction or elimination in undesiredreactions that can occur with such residues and impurities, as well asother benefits that are discussed or that can be understood by thoseskilled in the art from the disclosure provided herein.

The present invention permits that the dry compounded material achievedat step 20 can be used in a coating slurry based process as describedbelow. In blending step 22 of FIG. 1 a, an aqueous solution may be addedto the compounded dry fibrillized material that was created during dryfibrillization step 20. In one embodiment, the aqueous solution is usedto make a slurry, which can be used for application of the particles 12,14, and 16 during an electrode coating process. In one embodiment, thecompounded material provided by dry fibrillization step 20 is added to 2to 6 times its weight of deionized water.

In some cases, after adding an aqueous solution in step 22, clumps orchunks of compounded material may remain in the resulting suspension. Instep 24, if needed, the compounded material can be further mixed tohomogenize the compounded material so as to form a smooth slurry.However, because as was described previously, substantially no or noagglomerates of coalesced particles are preferably provided during step20, such further mixing is typically able to be avoided. Alternativeaqueous solutions (such as a mixture of water and organic solvents) andmeans and methods of homogenizing the compounded particles can also beused to form the slurry described herein. In step 26, the slurry formedin steps 22 and/or 24 may be applied to a current collector. In oneembodiment, the slurry is applied to the current collector using adoctor blade. Other alternative means and methods for applying theslurry, such as through a slot die, or a direct or reverse gravureprocess, can also be used in accordance with the present invention. Inone embodiment, the slurry can be applied to the current collector witha thickness of between 50 μm and 600 μm. A lesser or greater coatingthickness is also possible in other embodiments, which should be limitedonly by the claims and their equivalents. In one embodiment, the currentcollector comprises an etched or roughened aluminum sheet, foil, mesh,screen, porous substrate, or the like. In one embodiment, the collectorcomprises unetched foil. In one embodiment, the current collectorcomprises a metal, for example, copper, aluminum, silver, gold, and thelike. In one embodiment, the current collector comprises a thickness ofabout 10-50 microns. A lesser or greater collector thickness is alsopossible in other embodiments, which should be limited only by theclaims and their equivalents. Those skilled in the art will recognizethat if the electrochemical potential allows, other metals could also beused as a collector.

In one embodiment, prior to applying the slurry to a current collector,an added step 28 of treating the collector to improve adhesion betweenthe current collector and the applied slurry can also be performed. Forexample, the current collector can be coated with a bonding agent,layer, or adhesive to improve the adhesion of the slurry to thecollector. Carboxymethyl cellulose, melamine, phenolics, or furans canbe used as a bonding agent between the collector and slurry. In oneembodiment, adhesive coating sold under the trade name Electrodag®EB-012 by Acheson Colloids Company, 1600 Washington Ave., Port Huron,Mich. 48060, Telephone 1-810-984-5581 is used. Alternatively, otheradhesives or bonding agents can be used and/or other methods and meansfor improving the adhesion between the current collector and slurry canbe used, such as treating or physically roughening the surface of thecurrent collector prior to application of the slurry.

After the slurry is applied to the collector, it can be dried during adrying step 30 to form an electrode comprising the current collector andcoated slurry of dry fibrillized carbon 12, 14 and binder 16 particles.During the drying step 30, the aqueous solution is evaporated fromwithin the slurry, which results in the formation of a conductiveelectrode film on the current collector. In one embodiment, the slurryis dried in an oven at 85° C. for 1 hour. Alternatively, other methods,times, and temperatures for drying the slurry can be used.

In step 32, the electrodes can be compacted to densify the conductiveelectrode film and further fibrillate the compounded material. In oneembodiment, the film can be compacted using a calender device. Acompacting and/or calendering function can be achieved by a roll-mill,calender, a belt press, a flat plate press, and the like, as well asothers known to those skilled in the art. In one embodiment, thecalender device may comprises a roll-mill. A high-pressure nip at theentry to the roll-mill can be set to gradually decrease the filmthickness by 15% to 60% in 2 to 10 passes.

Weak fibrillization has been described above in the context of step 20(FIG. 1 a). However, it has been identified that further dryfibrillization may also occur during one or more of acompact/bonding/bonding step 32. After compaction/calendering, visibleformation of fibrils may occur. Such fibrillization may be effectuatedby the high pressure and shear forces that are known to exist and beapplied to the binder particles between calender rolls during theformation of dry films and/or electrodes. It is understood that theamount of shear and/or energy applied to at least some of the dryparticles is higher than during dry fibrillization step 20, and thatsuch shear forces are of sufficient magnitude to stretch and/or unwindthe binder present in the slurry to a point that fibrils become formedand are visible under an SEM. Applying high pressure and shear forcescan further reduce the separation distance between particles to, thus,increase attractive forces resulting from surface free energies. A“strong” type of fibrillization, thus can be made to occur in an amountthat results in the visible formation of fibrils. Slurry coated filmsmade in the manner described can be made with less agglomeration ofbinder that occurs in the prior art extrusion and coating processes. Itis believed that the substantial or total absence of agglomerates in afinal film product may be effectuated by a certain minimal threshold ofenergy and/or force imparted to the constituent dry particles during thepreviously described dry fibrillization step. In this manner, both weakand strong fibrillization of one or more of the particles describedherein contribute to the novel and new properties of the electrodes andfilms described herein.

Referring now to FIG. 2, and preceding Figures as needed, there is seenone possible apparatus for making a coating based electrode according tothe present invention. In one embodiment seen in FIG. 2, a slurry orsuspension made from dry fibrillized dry carbon and dry binder particles12, 14, and 16 can be held in a suspension feeder 34, and a currentcollector 36 in the form a roll of aluminum foil, coated if needed withan adhesive/bonding agent, can be held on a feeding roll 38. Thecollector 36 may be wrapped around a roller 39, positioned beneath acoating head 40 and adjacent to the suspension feeder 34. As thecollector 36 moves across the roller 39, a suspension of slurry is fedfrom the coating head 40 onto a surface of the collector 36. From there,the collector 36 is carried through an oven 42, which is configured forremoving any of the solution(s) used. The dried slurry forms aconductive electrode film on the collector 36. Next, the collector maybe fed through a series of rollers 44 configured to compact and calenderthe dried slurry and current collector so that densification and furtherfibrillization occurs. After calendering, a finished electrode 46 isgathered on a storage roll 48 where it may be stored until it isassembled into a finished energy storage device.

Referring now to FIG. 3, and preceding Figures as needed, duringmanufacture, one or more finished electrode 1200 coated with one or moreslurry made accordance with embodiments disclosed herein is rolled intoa configuration known to those in the electrode forming arts as ajellyroll. Not shown is a separator or other porous electricallyinsulating layer or film, disposed within the jellyroll, which acts toseparate layers of the rolled electrode 1200. The rolled electrode 1200is inserted into an open end of a housing 2000. An insulator (not shown)is placed along a top periphery of the housing 2000 at the open end, anda cover 2002 is placed on the insulator. During manufacture, the housing2000, insulator, and cover 2002 may be mechanically curled together toform a tight fit around the periphery of the now sealed end of thehousing, which after the curling process is electrically insulated fromthe cover by the insulator. When disposed in the housing 2000, theelectrode may be configured such that respective exposed collectorextensions 1202 of the electrode make internal contact with the bottomend of the housing 2000 and the cover 2002. In one embodiment, externalsurfaces of the housing 2000 or cover 2002 may include or be coupled tostandardized connections/connectors/terminals to facilitate electricalconnection to the rolled electrode 1200 within the housing 2000. Contactbetween respective collector extensions 1202 and the internal surfacesof the housing 2000 and the cover 2002 may be enhanced by welding,soldering, brazing, conductive adhesive, or the like. In one embodiment,a welding process may be applied to the housing and cover by anexternally applied laser welding process. In one embodiment, the housing2000, cover 2002, and collector extensions 1202 comprise substantiallythe same metal, for example, aluminum. An electrolyte can be addedthrough a filling/sealing port (not shown) to the sealed housing 1200.In one embodiment, the electrolyte is 1.4 M tetrametylammonium ortetrafluroborate in acetonitrile solvent. After impregnation andsealing, a finished product is thus made ready for commercial sale andsubsequent use.

Although the particular systems and methods herein shown and describedin detail are fully capable of attaining the above described objects ofthe invention, it is understood that the description and drawingspresented herein represent some, but not all, embodiments that arebroadly contemplated. Structures and methods that are disclosed may thuscomprise configurations, variations, and dimensions other than thosedisclosed. For example, capacitors as a broad class of energy storagedevices are within the scope of the present invention, as are, withappropriate technology based modifications, batteries and fuel cells.Also, different housings may comprise coin-cell type, clamshell type,prismatic, cylindrical type geometries, as well as others as are knownto those skilled in the art. For a particular type of housing, it isunderstood that appropriate changes to electrode geometry may berequired, but that such changes would be within the scope of thoseskilled in the art.

Thus, the scope of the present invention fully encompasses otherembodiments that may become obvious to those skilled in the art and thatthe scope of the present invention is accordingly limited by nothingother than the appended claims and their equivalents.

1. An electrode, comprising; a dry blend of dry carbon particles and drybinder particles subjected to shear forces, wherein the dry binderparticles are deposited onto and between the dry carbon particles with asurface energy sufficient to maintain contact and adhesion between thecarbon particles to support the dry blend of dry carbon and dry binderparticles.
 2. The electrode of claim 1, wherein the blend comprisesapproximately 50% to 99% activated carbon.
 3. The electrode of claim 1,wherein the blend comprises approximately 0% to 30% conductive carbon.4. The electrode of claim 1, wherein the blend comprises approximately1% to 50% fluoropolymer.
 5. The electrode of claim 1, wherein the blendcomprises approximately 50% to 99% carbon, approximately 0% to 30%conductive carbon, and approximately 1% to 50% fluoropolymer.
 6. Theelectrode of claim 1, wherein the electrode is a capacitor electrode. 7.The electrode of claim 6, wherein the electrode is a double-layercapacitor electrode.
 8. The electrode of claim 1, wherein the electrodeis a battery electrode.
 9. The electrode of claim 1, wherein theelectrode is a fuel-cell electrode.
 10. The electrode of claim 1,further comprising a current collector, wherein the binder and carbonparticles are in the form of a coated dried slurry, wherein the slurryis coupled to the current collector.
 11. The electrode of claim 1,wherein the dry binder particles are deposited onto and between the drycarbon particles via particle-to-particle collisions.
 12. The electrodeof claim 11, wherein the particle-to-particle collisions are introducedin a mill.
 13. The electrode of claim 12, wherein the mill comprises ajet mill.